In light of recent evidence from clinical studies that fewer postmenopausal women develop Alzheimer=s disease if they receive sex steroid replacement therapy, it has become important to examine the hypothesis that ovarian steroids can protect the brain from neurodegeneration. Interestingly, rhesus monkeys show many of the same aging-related cognitive impairments as do humans, and they also develop amyloid plaques in the same brain regions as do Alzheimer=s patients. The aim of this pilot project, therefore, was to determine whether female rhesus monkeys undergo true menopause, as do women, and if so to determine at what age this occurs. The results from this study clearly demonstrate that as female rhesus monkeys enter their third decade of life, they start to show irregular menstrual cycles which are associated with impaired ovarian steroidogenic function and a concomitant increase in circulating gonadotropin concentrations. The reproductive endocrine profiles of more th an twenty aged monkeys have been examined in detail, and the animals classified as having normal menstrual cycles, irregular cycles (perimenopausal) or as being acyclic (postmenopausal). These data clearly demonstrate that the aged rhesus monkey is a highly appropriate animal model in which to further investigate the potential neuroprotective effects of sex steroids. The data also provide a solid foundation for future studies using this valuable group of animals, including cognitive testing, hormone replacement, and ultimately neuropathology. FUNDING Alzheimer=s Research Alliance of Oregon PUBLICATIONS None